1. The Field of the Invention
The present invention is more specifically directed toward an apparatus and method for selectively heating and releasing medical substances from transdermal delivery systems and depot sites in or under a patient's skin or from injected or implanted controlled release systems.
2. The Background Art
Transdermal drug delivery affords users and patients distinct advantages over other delivery methods and techniques. Patients prefer transdermal administration in some cases because of the ease of administration and because transdermal drugs are delivered noninvasively. Care givers also appreciate the ease of administration and the ability to deliver a drug over a long period of time. Transdermal delivery in many cases avoids first pass elimination of drugs. Because of these advantages, transdermal drug delivery has grown in popularity and interest in studying transdermal drug delivery has increased.
Transdermal drug delivery occurs as a drug formulation is brought into contact with a patient's skin. In transdermal drug delivery, it often occurs that some of the drug gets stored in skin and sub-skin tissues after penetrating the skin. This effect is referred as “depot effect”, and the storage site as “depot” or “depot site” hereafter. As blood circulates through these tissues, the drug is absorbed into the blood stream and delivered throughout the systemic circulation. It is discovered that by placing heat on or near an administration site of a transdermally delivered drug, the heat will not only increase the skin's permeability, but also greatly increase the circulation in the tissues and have other effects that allow the drug to be absorbed more quickly into the systemic circulation. It has been suggested by the inventor that heat be used to increase onset time and to increase the amount of drug being absorbed into the skin.
Nothing in the prior art has taught that transdermal drug delivery is capable of rapidly responding to changing needs in a patient. The time it takes for the drug to be delivered from the drug formulation to the skin, be absorbed into the skin and surrounding tissues and from there absorbed into the systemic circulation and delivered throughout the systemic circulation has been seen as a barrier for rapid response or modification of the drug circulation in systemic circulation. Given this perception of transdermal drug delivery, techniques such as patient controlled analgesia (PCA) have not been attempted using transdermal drugs. Patient controlled analgesia may require the ability of the patient to choose when a particular dosc will be delivered, the ability of the care giver to set or prescribe the amount that will be delivered rapidly on demand, and the ability to prevent or lock-out the patient from excessively self-dosing.
In addition to the perceived physiological barriers to rapidly delivering drugs transdermally, the technology used in conjunction with transdermal drug delivery as taught in the prior art is not capable of sophisticated delivery techniques such as PCA. Current PCA treatment requires both sophisticated medical instruments and trained personnel. Current technologies are invasive, require carefully calibrated pumps and other equipment, all of which can be expensive. It would be advantageous therefore to develop a transdermal drug delivery system, which can rapidly respond to a patient's changing needs, that could deliver an additional drug dose quickly (referred to as bolus drug hereafter), and that could allow a patient to control the delivery of the additional drug on demand that can allow the caregiver to prescribe how much extra drug the patient can obtain from self dosing, and that could allow the caregiver to set “lock-out” times to prevent the patient from excessively self-dosing. (Lock-out time is the time period in which no extra drug is delivered even if the patient triggers the self-dosing mechanisms.)
The present invention also provides for extended duration of drug delivery limited only by the supply of drug and availability of electric current. The present invention also provides the ability to vary intervals at which extra drug is delivered and the length of time by which the drug is delivered. The present invention also provides the ability to let the caregiver to set “lock-out” time. This can be accomplished through use of a microprocessor in conjunction with the electric healing component. The present invention provides the ability to respond quickly to the patient's need and provide the patient a drug dose on demand in a safe and effective manner. By using the present invention as described in the methods herein, a patient can self-administer analgesia (PCA) or other drugs where appropriate. The present invention allows the user a greater variety of methods of use and provides additional reliability such as more precise control over the areas, either the temperatures at which they are heated and the duration for which they are heated. The present invention provides a variety of temperature profiles. The present invention does not require the continued replacement of the heating element.
It should be pointed out that the methods and apparatus presented in this invention may provide extra drug from controlled release formulations or devices implanted or injected into the skin or sub-skin tissues. In other words, the user may create a “depot site” by implanting or injecting drug into the skin and sub-skin tissues.